I don't know Bonaire nor Curacão... but I also would like to hear more on where there is a good, cheap snorkel trip. By cheap thus I'm saying shore snorkeling - if one takes a boat it's no longer "cheap".
As far as snorkeling is concerned, IMO:
Aruba only offers the Baby Beach area, which is far form the hotels... the rest of the island I found no good snorkeling at all (again, not considering a boat to the small day island).
DR I found no worthy shore snorkelling.
Cayman is NOT for snorkelling. There is the one shore dive entry site on the NW corner (at the turtle farm, there's a dive op there) that one could snorkel, and one might snorkel close to the SE corner (seasonal) - but I never found anything worthy of making a snorkel trip (if diving isn't one's primary motive). Does anyone know of something I missed?
Hawaii is of course awesome, a killer, fantastic shore snorkelling destination... but the accomodation costs likely make it impossible to call 'cheap'.
Bahamas I don't know all that well - I've dove the SW Nassau (Stuart's Cove - great sharks) and Abacos - but I haven't found any great snorkelling, and the spots we snorkelled from our boat while doing regatta in Abacos was less than average. I suspect I don't know the right spots and there are good ones??
Keys - well, I live here, have a boat, and I am not aware of ANY shore snorkelling.
Mexico
Cozumel - not great for snorkelling if diving isn't you main focus (diving is spectacular).
Cancun - I don't know it, but I haven't read anything to make me think if offers a worthy snorkel trip.
Akumal - Very nice bay to snorkel, I also stayed at Bahia something... and I saw turtles and rays (common or eagle) on every single entry!
Other south of Cancun to end of Riviera - I don't know, but I hope to learn something here!
Jamaica - Never been, but it is cheap for air and accomodations.
PR - Never been, but I do wonder about it as there is cheap air.
San Andres and Providencia - No worthy snorkelling but nice diving.
So, where are the best CHEAP/shore snorkel trip options?
Bay Islands (Honduras)? CR Caribbean? Turks and Caicos? Santa Marta (Colombia)? Ft. Lauderdale?